Use of induction motors in the home workshop - updated Iss2

[tisdai]

Thanks for the info Bob, great of you to post it here for everyone

Dave

 

[Geofrey]

Well I am new on the forum and my first place to stop is here. Very great work. Thanks.

 

[9fingers]

Thanks Geofrey and welcome to the forum.

One thing to bear in mind is that power distribution is a bit different in the US than in UK/Europe so some of the voltages will seem a bit strange.
I've not managed to get my head around how it is done in the US - I'm just aware that it is different. One day I must put in the effort to understand how it is done on your side of the pond.
So many things to learn and so little time!!

Good luck

Bob

 

[waveman2010]

Any one not wishing a nerdy comment stop reading but here goes. The single to 3 phase inverter will still deliver 240v per phase but only if referenced to a neutral point (that's why its called a neutral). between the phases it will be delivering 415V. what the inverter actually does is to split the 240 supply into three and then shift them 120 deg out of phase with each other, imagine 3 sine waves all peaking at different times. If you add all three voltages together at any one point on the cycles you get 415V. The current drawn from the 240V supply is distributed across the three phases in the machine itself but as Geofrey points out in his excellent artical you don't get something for nothing and the inverters them selves will draw a significant current. The actual voltage across the machine windings is very small held back by the generation effect of the motor all the torque being delivered by current. This is why machines burn when they are overloaded the speed is reduced so far that the back voltage its called the back EMF, does not balance the winding voltage far enough and the resulting rise in current heats up the machine. this effect can damage machines on start up so the star delta starter system manages the start up voltages till the motor is up to speed. The newer soft start starters use still more devices similar to the inverters to limit the power taken by a machine on start up. Hope this was of interest to anyone with a liking for AC power systems.... mmmmmmm.

 

[Jonzjob]

That is all true for star wound, but delta still has an output of 240v and no neutrals :mrgreen: :mrgreen:

Mine's delta :roll:

 

[karl530]

Hi Bob,

There is a wealth on knowledge in this thread and in you own articles, I Have a question pertaning to phase converter design.
In most of the circuits I have seen when there is a need to step-up the voltage (240V to 415) a autotransformer has been employed for this job. Looking at the cost an autotransformer is about 3x more than a equivalent kva isolation transfomer. Would it possible to use an isolation unit in place on the auto unit?

Regards Karl

 

[9fingers]

Hi Karl,

I'd be interested in seeing the prices that you base your comments on

I have not found 415/240 isolating transformers cheaply with any useful power rating for this application.

Auto transformers are use in converters as they are cheaper to make for a given power - less copper used

A simple 240 in 240 out transformer can be wired to be an auto transformer but the voltage will be too high at 480v. You might find one with a tapped secondary to get nearer 440v which will be the maximum for the motor.
Another trick is to get two 240 in 110v out safety transformers. wire the secondaries in series, and the primaries in parallel in phase. You MUST never connect the earth to either transformer which is no problem with the plastic cased ones. You then put the two series outputs in series with the primaries making sure once again that the phasing is correct. This provides 460v from 240 which is still a bit high but if you mains supply is nearer 220 or 230 then the output is almost correct.

It does not matter how you get the voltage step up as long as it is roughly in the ratio 1:sqrt3 or about 1:1.73

If your motor is capable of delta connection for 240v 3 phase operation then the converter becomes trivial as no transformer is needed.

Bob

 

[karl530]

Hi Bob,

That was a speedy reply! I based my price on those given on the airlink transformer website, but upon closer inspection I have realised it was torodial transformers I was looking at not enclosed isolation units d'oh! The transformers I have been looking at are below

AU5004 - Enclosed Autowound transformers Part number: AU5004 £212
VA: 5000
Input vac: 415
Output vac: 230
Regulation: 0%
Case: P4 Grey Steel case IP23
Dimensions: Ht:270 L: 338 W:215 (mm) Weight: 20kg
Surge protection: SL35 Surge protection
Type: Autowound transformer Conforms to EN61558-2-13 CE & RoHS
Input Termination: 3 M6 studs
Input notes This an autotransformer and may be used to stepup or stepdown

Not that badly priced just that the primary and secondarys are in 'reverse' for the application needed which I am not sure if that matters but there is a not saying it is step up or down.

Also the below which is a chassis mount type torodial.

CM5000176 - Standard Range Toroidal Transformers Part number: CM5000176 £180
VA: 5000
Input vac: 415 Input current amps: 21.70
Output vac: 230 Output current amps: 21.70
Regulation: 3%
Dimensions: OD: 240 Ht: 110mm Weight: 22kg
Type: Safety Isolating transformer Conforms to EN61558-2-23 CE & RoHS
Input Termination: 200mm Flexible leads 14awg
Output Termination: 200mm Flexible leads 14awg
Fixings: Fixing Potted centre Drilled 10mm

The reason I ask these questions is because I have a whitehead 2.5hp 415 table saw and a oliver 415v RAS but the motor HP is unkown on the oliver, my guess 3 or 4hp. I have seen a 240v to 415v VFD but I have been lead to believe that they are 'custom' modified units. As they are the same in appearance as the teco 7200 ma series but as far as I can tell no units offering the above voltage increase exist on their website.

Regards Karl

 

[9fingers]

The prices look a lot closer than 3 :1 but anyway

Sounds like you have been looking at inverters from Drives Direct. Provided the modified inverter is rated around twice the output that you need, the modified inverters should work OK. I've modified a few recently myself and they seem to work oK but I've yet to give them a thorough testing.

If you want to go down the converter route, then adding a motor to make a rotary converter should enable it to run either of your machines.

Bob

 

[karl530]

The prices look a lot closer than 3 :1 but anyway

Sounds like you have been looking at inverters from Drives Direct. Provided the modified inverter is rated around twice the output that you need, the modified inverters should work OK. I've modified a few recently myself and they seem to work oK but I've yet to give them a thorough testing.

If you want to go down the converter route, then adding a motor to make a rotary converter should enable it to run either of your machines.

Bob

They are closer than 3:1 it's get to late for me to think straight and I have been trying to get my head round the most suitable way to power these machines, I have spoken to David at drives direct, I got the impression that the VFD was ok to be matched to the maximum motor HP so for the RAS if it is indeed 3HP then a 3HP drive would be ok (bit it is an unkown at the moment, so it would be prudent to overate the unit driving it anyway), though I assume it would be running to the max capability of the drive.

The main factor for me though is the costs involved, i reckon I can build a RPC for alot less than a VFD would cost.
Out of the 2 transformer mentioned in my last post, is one more suitable for a phase converter than the other?

Sorry about all the questions!

Karl

 

[9fingers]

Either transformer would do the job for your RPC. Might as well go for the cheapest.

I reckon that if an inverter is modified for voltage conversion, it should be de-rated - usually by around 2:1

Dave guarantees his products so you should have some comeback if it does not work as expected.
He does mark up the prices for his voltage conversion mods because he can. The change is nothing special, it is just a case of changing the rectifier configuration to a voltage doubler. The derating is necessary as the reservoir is topped up less frequently than with a three phase input. If you add further capacitors to the reservoir bank then no de-rating should be needed.

Bob

 

[drmartin1981]

Hi Bob,

I'm currently using a JET band saw with an induction motor on it, Im a novice with reguards to motors so found your write up very informative and helpful in understanding exactly what I'm using.

Im happy with the performance of the induction motor!

 

[9fingers]

Hi Bob,

I'm currently using a JET band saw with an induction motor on it, Im a novice with reguards to motors so found your write up very informative and helpful in understanding exactly what I'm using.

Im happy with the performance of the induction motor!

Thanks for taking the trouble to post.

If you get any future problems with induction motors, just give me a shout and I'll try and sort out a solution.

Bob

 

[Retired]

Hi,

What a great thread Bob; very useful and informative indeed and many thanks for going to the trouble to add it.

It brings back many memories for me seeing the Brook Crompton nameplate. I worked for this company (Brook Motors) here in Huddersfield for 24 years up to my early retirement in 2000. At the height of production we manufactured over 1,000 motors through No5 Home Trade Despatch and around 300 motors through No6 Export per day.

The company had a number of manufacturing facilities in the UK; Honley and Doncaster factories supplied small or fractional HP motors; the main factory and headquarters where I worked at St Thomas Road in Huddersfield and our Electrodrives factory in the Midlands supplied medium sized motors and the Guiseley factory supplied the big motors. Bull in Ipswich supplied the DC motors.

No5 Despatch became the main distribution hub; motors would arrive from the other factories and be consolidated into loads. Motors with gearboxes fitted; motors with inverters fitted; spares and repairs all came from across the road from our other departments; control gear came from the Wakefield factory.

My job was to ensure everything was in place ready for the night loaders and boy it was a stressful job; I lived and breathed electric motors 365 days a year as I couldn't switch off; in the end I came down with shingles and this was the sign to call it a day whilst I still could; I volunteered for redundancy and took my works pension retiring from active conflict aged 53 in 2000.

Unfortunately like many UK companies Brook's phased out manufacturing in the UK moving this abroad; the company is now a distribution centre having a large well stocked warehouse and customers can still have any motor modified quickly to order.

I don't wish to hi-jack your excellent thread Bob but since retiring I've been even more busy and one job I have done is to install 3 phase 415V up to 10HP in our garage allowing me to run single or multiple machines up to the 10HP. These machines can be switched on and off just as if proper 3 phase had been laid on. I hope you are sitting down because not only does this give full power but it only cost me just under £120 for the entire installation. One guy I know wanted to have 3 phase 415V installed into his two farmhouses to power heat pumps in Wales and the local supply company quoted him over £17,000. As a new member to this forum I'd like to settle in before adding all the details in a new thread as I might need to gain permission to add an important link.

This is the best write up on motors I've seen Bob and top marks to you.

Kind regards, Col.

 

[devonwoody]

Welcome to the forum and I and others look forward to having your experience here, and also wish you a happy retirement.

 

[Retired]

Hi,

Many thanks for your welcome and good wishes devonwoody; they are much appreciated. For the last ten years I've been collecting and restoring vintage radios but now I am having a good clear out and want to concentrate on furniture/cabinetmaking for our own use. I've just completed a new computer desk and hopefully will add this shortly.

Kind regards, Col.

 

[Camoz]

Hi,

Just wanted to say great post a wealth of knowledge.

Thanks,

Camoz

 

[Maurice Sheehan]

Is this pdf still available somewhere?

 

[Ttrees]

Is this pdf still available somewhere?

'Tis the best info you'll find, and freely available to download, not here though, but another forum,
not called "the other place" as you might have seen written before.
I guess there might be some hints to google, if you search that quoted term in the top.

 

[Spectric]

What information are you looking for ?